CD20-positive T-cell large granular lymphocyte leukemia: case report and review of the literature

CD20+ T cells: an emerging T cell subset in human pathology

Introduction

Although CD20 is classically a B cell marker, in the last three decades, dim expression has been noted on a subset of T cells as well that has been independently verified by a number of groups. Our understanding of these cells and their function is not well established.

Methods

A thorough review of original articles on CD20⁺T cells was undertaken of Pubmed by using combination of phrases including “CD20⁺”, “CD20-positive” and “T cells”. Articles in English were considered, and there was no time restriction.

Results

CD20⁺T cells express the standard T cell markers and, in comparison to CD20¯ T cells, appear to express greater inflammatory cytokines and markers of effector function. Although the ontogeny of these cells is still being established, the current theory is that CD20 may be acquired by trogocytosis from B cells. CD20⁺T cells may be found in healthy controls and in a wide range of pathologies including autoimmune diseases, haematological and non-haematological malignancies and human immunodeficiency virus (HIV) infections. One of the best studied diseases where these cells are found is multiple sclerosis (MS) where a number of therapeutic interventions, including anti-CD20 depletion, have been shown to effectively deplete these cells.

Conclusion

This review summarises the latest understanding of CD20⁺T cells, their presence in various diseases, their putative function and how they may be an ongoing target of CD20-depleting agents. Unfortunately, our understanding of these cells is still at its infancy and ongoing study in a wider range of pathologies is required.

Aberrant CD20 expression in angioimmunoblastic T-cell lymphoma

We report on a 60-year-old man, having angioimmunoblastic T-cell lymphoma (AITL) with aberrant expression of CD20. The initial biopsy specimen showed features of AITL with the typical CD3(+)CD20(-) immunophenotype. As the disease progressed, biopsy specimens of the recurrent lesions showed unusual results for AITL with the CD20(+) immunophenotype in both flow cytometry and immunohistochemistry analysis. Double immunostaining confirmed that the lymphoma cells were simultaneously positive for CD3 and CD20. The disease became resistant to combined chemotherapies and the patient died 3 years after the initial diagnosis. Autopsy revealed a composite of AITL and EBV-positive diffuse large B-cell lymphoma. Although it is unknown whether the instability of the CD20 antigen expression is correlated with the behaviour of AITL, the administration of rituximab should be considered as an alternative therapeutic option in such cases.